Together with an improvement of capability of data storage, document image processors rapidly become popular in which a paper document read from a scanner and etc. is stored and managed as a document image that is image data of the document.
It is arranged in such document image processor that each document image is registered corresponding to character strings that are document tag information like a keyword or a title, in order to search a desired document image from plural document images stored in a data storage.
FIG. 19 shows the document tag information conceptually. As shown in the drawing, the document tag information, such as “Confidential” 191, “A-company” 192, “Year 1999” 193 and “New car” 194, for example, acts as a keyword for a document image 190. Provided that a plurality of document tag information is attached to each document image in this way, it is possible to search a desired document image by limiting those plural document tag information.
In a conventional way, a user has inputted by hand those document tag information at storing of the document image. When the user input the document tag information, however, if the number of documents increases, the workload becomes large. Accordingly, such inputting operation is quite impractical. So in recent years the other apparatus has appeared that is able to recognize characters on the document image, handle a recognized character string as document tag information, and then attach the document tag information to the document image without assistance of hand labor.
For instance, Japanese laid-open publication No. 8-147313 discloses a method of using a mark sheet. In the method, first, a user checks off a check box of document tag information to be attached to a document image, the document tag information described on the mark sheet in a specific form. The mark sheet is read by a document image processor before the paper document is read, whereby the document tag information to be attached can be specified from the nominees of document tag information registered in advance. The method does not require a use of an input device such as a keyboard or a pointing device, and it is possible to attach the document tag information automatically to the document image to be registered.
Incidentally, it is very important for an effective searching of document images to give appropriate document tag information to the document images. Specifically, a general searching method is to specify document tag information corresponding to a desired document image from a list of plural document tag information displayed on a screen. And in order to specify such document tag information quickly, respective document tag information should express the contents of the document directly.
The Japanese Laid-open Publication No. 8-202859 discloses another method wherein a region including a title-character string (which is called a “title region” hereafter) is extracted from a document image, and the characters in the image of the title region is recognized, and then a recognized title-character string is made to document tag information. Since the title-character string represents the contents of the document directly, an image data processor adopting the title-region extracting method can quickly specify the document tag information corresponding to the desired document image.
The above method of extracting the title region, which is disclosed in Japanese laid-open publication No. 8-202859, is based on the aspect that the title characters are in the largest size among all of characters included in the document image. After dividing the document image into plural regions (a region to which consecutive character rectangles are combined), and calculating an average of character size in the respective regions, a region in which the average of character size is the maximum is extracted as a title region. Accordingly, it is natural that the title-region extracting method extracts only one title region for a document image.
However, if there are plural documents with the similar contents, the documents always have the similar titles each other. Therefore, the conventional title-region extracting method had a problem that, when there are plural documents with similar contents, it is impossible to quickly specify the document tag information corresponding to the desired document image.
In order to avoid the above problem there is a method without attaching similar titles to documents at preparing paper documents. However, it is undesirable to request a user to do the preparatory operation.
On the other hand, the method in Japanese laid-open publication No. 8-147313, which uses a mark sheet, has a very troublesome work that it is necessary to define the form of the mark sheet describing all items of the document tag information, and to define the reading method of the mark sheet, when a document image processor is configured as the software. In addition, in case of adding and registering nominees of new document tag information later on, the items of document tag information are changed. Thereby, it is necessary to reconstruct the form of the mark sheet and the reading method.
In addition, in case of using the mark sheet, since the user always uses the same sheet to check off the check box, it is hard for a user to visually confirm which document tag information is attached to the document image, and it causes inputting mistakes frequently.
The invention is proposed taking the above problems into consideration, and has an object to provide the document image processor for extracting title regions and marks attached to a document image by the user from a document image to use them as document tag information, and to provide the method for extracting document titles, and the method for imparting document tag information.